Aluminum alloy foil

ABSTRACT

An aluminum alloy foil is provided that is used as a material of a container and that achieves desired heat-resistant properties, enabling the container to withstand repeated use. The aluminum alloy foil is configured so as to: maintain a tensile strength of at least 120 N/mm2 and have an elongation of at least 2.0% when subjected to softening treatment at 150° C. for a maximum of 240 minutes; maintain a tensile strength of at least 100 N/mm2 and have an elongation of at least 3.0% when subjected to softening treatment at 180° C. for a maximum of 240 minutes; and maintain a tensile strength of at least 90 N/mm2 and have an elongation of at least 3.0% when subjected to softening treatment at 200° C. for a maximum of 240 minutes.

TECHNICAL FIELD

The present invention relates to an aluminum alloy foil, a container into which the aluminum alloy foil is formed, and a method for producing the aluminum alloy foil.

BACKGROUND ART

As a baking mold for baking contents such as a cake or bread, a container into which an aluminum alloy foil is formed has been conventionally used, as described in Patent Document 1 listed below.

Such containers cannot withstand repeated use because they tend to lose strength owing to the heat given thereto when the contents are baked, with the result that they are warped or deformed when, for example, the contents are removed.

For example, in the case where the contents constitute a cake or bread, a baking temperature of 150 to 200° C. and a baking time of 15 to 30 minutes are generally used. After the cake or bread is baked at such temperature for such baking time, it is highly probable that the container will be warped or deformed by a force applied when the baked cake or bread is removed from the container.

Accordingly, it is impossible to reuse the container for the subsequent baking, and each container has to be disposed of at every baking process, resulting in higher cost.

PRIOR ART REFERENCE Patent Document

-   Patent Document 1: JP 2000-079934 A

SUMMARY OF THE INVENTION Technical Problem

The cost of baking the contents can be reduced if properties of an aluminum alloy foil to be formed into a container are modified so that the container is prevented from reducing its strength when the contents are baked and is reusable a plurality of times.

For example, for a container of a cake or bread, the industry has a desire to reuse the container about four or five times, which is expected to lead to significant cost reduction.

Accordingly, a problem addressed by the present invention is to provide an aluminum alloy foil that is used as a material of a container and that achieves desired heat-resistant properties, enabling the container to withstand repeated use.

Solution to Problem

An aluminum alloy foil according to the present invention adopted to solve the aforementioned problem is configured so as to: maintain a tensile strength of at least 120 N/mm² and have an elongation of at least 2.0% when subjected to softening treatment at 150° C. for a maximum of 240 minutes, maintain a tensile strength of at least 100 N/mm² and have an elongation of at least 3.0% when subjected to softening treatment at 180° C. for a maximum of 240 minutes, and maintain a tensile strength of at least 90 N/mm² and have an elongation of at least 3.0% when subjected to softening treatment at 200° C. for a maximum of 240 minutes.

When used as a container for baking its contents at a generally used temperature for a generally used time, the aluminum alloy foil configured as above according to the present invention can maintain an adequate strength to prevent the container from warping or deforming when the contents are removed after baked.

The aluminum alloy foil according to the present invention preferably contains: 0.3 to 3.0 mass % iron; 0.8 to 1.5 mass % silicon; 0.0001 to 0.011 mass % copper; 0.0001 to 0.6 mass % manganese; 0.0001 to 0.011 mass % magnesium; 0.001 to 0.011 mass % zinc; 0.005 to 0.5 mass % titanium; and 0.0001 to 0.3 mass % zirconium, with the balance being aluminum and inevitable impurities.

The aluminum alloy foil configured as in the composition described above according to the present invention can prevent large-diameter crystallized products from occurring in the alloy, thus contributing to creation of a foil having an adequate strength.

The aluminum alloy foil according to the present invention is preferably subjected to intermediate annealing at a temperature of 300° C. to 400° C. during plate-rolling into a thickness of 0.5 to 1.2 mm after continuous casting. The aluminum alloy foil preferably has a thickness of 5 to 100 μm.

Configuring the aluminum alloy foil according to the present invention through heat treatment as described above ensures that the foil is balanced between tensile strength and elongation.

A container according to the present invention is preferably includes the aluminum alloy foil described above.

As a matter of course, the alloy foil according to the present invention can be used for applications other than containers, such as electronic components.

A method for producing the aluminum alloy foil according to the present invention preferably includes the steps of:

preparing an aluminum alloy containing: 0.3 to 3.0 mass % iron; 0.8 to 1.5 mass % silicon; 0.0001 to 0.011 mass % copper; 0.0001 to 0.6 mass % manganese; 0.0001 to 0.011 mass % magnesium; 0.001 to 0.011 mass % zinc; 0.005 to 0.5 mass % titanium; and 0.0001 to 0.3 mass % zirconium, with the balance being aluminum and inevitable impurities; forming the aluminum alloy into an aluminum alloy piece through continuous casting; plate-rolling the aluminum alloy piece into an aluminum alloy plate having a thickness of 0.5 to 1.2 mm; carrying out intermediate annealing at a temperature of 300 to 400° C. during the plate-rolling step; and foil-rolling the aluminum alloy plate into an aluminum alloy foil having a thickness of 5 to 100 μm.

Effects of the Invention

Because of being configured as described above, the aluminum alloy foil according to the present invention maintains an adequate strength even after subjected to softening treatment at a predetermined temperature for a predetermined time. Therefore, a container into which the aluminum alloy foil is formed can withstand repeated use for baking contents of the container.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph indicating tensile strength properties of aluminum alloy foils after heated at 150° C.

FIG. 2 is a graph indicating elongation properties of aluminum alloy foils after heated at 150° C.

FIG. 3 is a graph indicating tensile strength properties of aluminum alloy foils after heated at 180° C.

FIG. 4 is a graph indicating elongation properties of aluminum alloy foils after heated at 180° C.

FIG. 5 is a graph indicating tensile strength properties of aluminum alloy foils after heated at 200° C.

FIG. 6 is a graph indicating elongation properties of aluminum alloy foils after heated at 200° C.

DESCRIPTION OF EMBODIMENTS

An aluminum alloy foil according to an embodiment of the present invention will now be described.

The aluminum alloy foil of the embodiment has the following tensile strength and elongation properties when subjected to softening treatment at a temperature of 150° C. to 200° C.

When subjected to softening treatment at 150° C. for a maximum of 240 minutes, the aluminum alloy foil maintains a tensile strength of at least 120 N/mm² and has an elongation of at least 2.0%.

When subjected to softening treatment at 180° C. for a maximum of 240 minutes, the aluminum alloy foil maintains a tensile strength of at least 100 N/mm² and has an elongation of at least 3.0%.

When subjected to softening treatment at 200° C. for a maximum of 240 minutes, the aluminum alloy foil maintains a tensile strength of at least 90 N/mm² and has an elongation of at least 3.0%.

The aluminum alloy foil holding these properties according to the embodiment can be obtained by using a production method according to an embodiment described below to produce an aluminum alloy foil whose example composition is shown below.

Although no particular limitation is imposed on the composition of the aluminum alloy foil of the embodiment, the composition is preferably as follows:

The aluminum alloy foil contains:

0.3 to 3.0 mass % iron (Fe);

0.8 to 1.5 mass % silicon (Si);

0.0001 to 0.011 mass % copper (Cu);

0.0001 to 0.6 mass % manganese (Mn);

0.0001 to 0.011 mass % magnesium (Mg);

0.001 to 0.011 mass % zinc (Zn);

0.005 to 0.5 mass % titanium (Ti); and

0.0001 to 0.3 mass % zirconium (Zr).

The balance is made up of aluminum (Al) and inevitable impurities.

Iron, which is included in the foregoing composition, crystallizes out as an Al—Fe based compound in an aluminum alloy to contribute to improvement of the elongation of the aluminum alloy foil.

When the iron content is less than 0.3 mass %, the effect of improving the elongation may not be fully obtained.

When the iron content exceeds 3.0 mass %, the iron may crystallize out as an Al—Fe based compound in an excessive amount to increase the tensile strength too much, resulting in a lower elongation.

Silicon, which is included in the foregoing composition, contributes to improvement of the tensile strength of the aluminum alloy foil.

When the silicon content is less than 0.8 mass %, the effect of improving the tensile strength may not be fully obtained.

When the silicon content exceeds 1.5 mass %, the tensile strength may increase too much, resulting in a lower elongation.

Copper, which is included in the foregoing composition, tends to form a solid solution with aluminum to reduce the elongation of the aluminum alloy foil.

Thus, the copper content is preferably limited to 0.011 mass % or less. More preferably, the copper content is 0.005 mass % or less. Although no particular limitation is imposed on the lower limit of the copper content, the lower limit is usually about 0.0001 mass %.

Manganese, which is included in the foregoing composition, contributes to improvement of the tensile strength and elongation of the aluminum alloy foil.

However, manganese may crystallize out as an Al—Mn based compound in an excessive amount in an aluminum alloy to increase the tensile strength of the aluminum alloy foil too much, resulting in a lower elongation of the aluminum alloy foil. Thus, the manganese content is preferably limited to 0.6 mass % or less. Although no particular limitation is imposed on the lower limit of the manganese content, the lower limit is usually about 0.0001 mass %.

Magnesium, which is included in the foregoing composition, tends to form a solid solution with aluminum to reduce the elongation of the aluminum alloy foil.

Thus, the magnesium content is preferably limited to 0.011 mass % or less. More preferably, the magnesium content is 0.005 mass % or less. Although no particular limitation is imposed on the lower limit of the magnesium content, the lower limit is usually about 0.0001 mass %.

Zinc, which is included in the foregoing composition, contributes to improvement of the tensile strength and elongation of the aluminum alloy foil, but significantly reduces corrosion resistance of the aluminum alloy foil.

Thus, the zinc content is preferably limited to 0.011 mass % or less. Although no particular limitation is imposed on the lower limit of the zinc content, the lower limit is usually about 0.001 mass %.

Titanium, which is included in the foregoing composition, contributes to improvement of the tensile strength and elongation of the aluminum alloy foil.

When the titanium content is less than 0.005 mass %, the effect of improving the tensile strength and elongation may not be fully obtained.

When the titanium content exceeds 0.5 mass %, the tensile strength of the aluminum alloy foil may increase too much, resulting in a lower elongation.

Zirconium, which is included in the foregoing composition, contributes to improvement of the tensile strength and elongation of the aluminum alloy foil.

When the zirconium content is less than 0.0001 mass %, the effect of improving the tensile strength and elongation may not be fully obtained.

When the zirconium content exceeds 0.3 mass %, the tensile strength of the aluminum alloy foil may increase too much, resulting in a lower elongation.

Although no particular limitation is imposed on the thickness of the aluminum alloy foil of the embodiment, the aluminum alloy foil is preferably 5 to 100 μm thick.

When the thickness is smaller than 5 μm, a pinhole may be made in the foil. When the thickness exceeds 100 μm, an excessive strength of the foil may make the foil less formable.

Although no particular limitation is imposed on a method for producing the aluminum alloy foil of the embodiment, the following production method is preferably used.

First, an aluminum alloy in the foregoing composition is prepared.

The aluminum alloy is cast by using a known continuous casting process to obtain an aluminum alloy piece in the form of a plate having a thickness of 6 mm.

Next, the aluminum alloy piece is plate-rolled by using a known cold rolling process to obtain an aluminum alloy plate having a thickness of 0.5 to 1.2 mm.

The aluminum alloy plate is further foil-rolled by using a known cold rolling process to obtain the aluminum alloy foil having a thickness of 5 to 100 μm according to the embodiment.

A method for producing the aluminum alloy foil according to the embodiment further includes carrying out intermediate annealing at an annealing temperature of 300 to 400° C. for an annealing time of 2 to 48 hours during the plate-rolling step.

As an example, and without limitation, intermediate annealing may be carried out on an aluminum alloy plate having a thickness of 1.2 mm at 170° C. and 400° C. for five hours, while intermediate annealing may be carried out on an aluminum alloy plate having a thickness of 0.5 mm at 300° C. and 500° C. for five hours. The intermediate annealing was carried out under an air atmosphere, but alternatively it may be carried out under an inert gas or vacuum atmosphere.

As an example, the aluminum alloy plate having undergone the intermediate annealing may be rolled to a thickness of 75 μm during the subsequent foil-rolling step.

The intermediate annealing makes it easy to adjust the balance between the tensile strength and the elongation of the aluminum foil finally obtained, so that the balance becomes optimum for a container made of the foil to withstand repeated use when the container is used for baking contents of the container.

In the case where a coiled aluminum foil weighing 500 kg or more is treated, when the annealing temperature is lower than 300° C. or the annealing time is shorter than two hours, the winding core may fail to reach the temperature. When the annealing temperature is higher than 400° C. or the annealing time is longer than 48 hours, the tensile strength outside the winding may be inadequate.

A container of an embodiment can be obtained by forming the aluminum alloy foil of the embodiment into the container by using a known forming method such as press work.

Although no particular limitation is imposed on applications of the obtained container, the container is suitably used as a container of a cake or bread to be baked in an oven or the like.

Owing to the tensile strength and elongation properties of the aluminum alloy foil of the embodiment as described above, the container has an adequate strength and is prevented from warping or deforming when the contents such as bread are removed, and thus the container can be repeatedly used for subsequent baking operations. Consequently, the aluminum alloy foil can contribute to reduction in cost of producing bread or the like.

Although no particular limitation is imposed on the shape of the container, by way of example, the container may include a bottom wall in a circular or similar shape in plan view, a peripheral wall rising from the rim of the bottom wall, a flange horizontally extending from the rim of the peripheral wall, and a curling added to the outer edge of the flange.

Note that applications of the aluminum alloy of the embodiment is not limited to containers, and the aluminum alloy may be suitably used to be formed into an article other than containers, such as an electronic component.

Examples

The present invention will now be made clearer by Examples and Comparative Examples provided below.

An aluminum alloy piece in the alloy composition shown in Table 1 below was obtained by continuous casting, and then plate-rolled into a 0.5 mm thick aluminum alloy piece, which was then subjected to intermediate annealing at a temperature of 300° C. for five hours. Resultant aluminum alloy foils each having a thickness of 75 μm were obtained as Examples 1 to 3.

In addition, an aluminum alloy piece in the alloy composition shown in Table 1 below was obtained by continuous casting, and then plate-rolled into a 1.2 mm thick aluminum alloy piece, which was then subjected to intermediate annealing at a temperature of 400° C. for five hours. Resultant aluminum alloy foils each having a thickness of 75 μm were obtained as Examples 4 to 6.

Concerning content ranges for the individual elements in Table 1 below, ranges for chemical components for preparing an alloy in a large melting furnace with process capability taken into consideration are defined as the ranges specified in claim 2 in the appended claims.

TABLE 1 Si Fe Cu Mn Mg Zn Ti Zr Chemical 1.27 1.54 0.0011 0.0098 0.0004 0.0028 0.022 0.15 components (mass %)

An aluminum alloy piece having the alloy impurity of 1N30 (JIS H 4160-1994) was obtained by continuous casting, and then plate-rolled into a 0.5 mm thick aluminum alloy piece, which was then subjected to intermediate annealing at a temperature of 300° C. for five hours. Resultant aluminum alloy foils each having a thickness of 75 μm were obtained as Examples 7 to 9.

These aluminum alloy foils of Examples 1 to 9 were formed by deep drawing into baking mold containers each in the shape of a circle in plan view having an opening outer diameter of 75 mm, a bottom diameter of 50 mm, and a height of 50 mm.

Bread dough was put into each container and baked in a generally used convection oven.

The baking temperature was 150° C. for Examples 1, 4, and 7, 180° C. for Examples 2, 5, and 8, and 200° C. for Examples 3, 6, 9. The baking time was 30 minutes for every Example.

The bread baking operation was repeated on each of the baking mold containers of Examples 1 to 9, and the number of times each container can be reused was evaluated. Results are shown in Table 2 below. To determine the number of reuse times, a container was regarded as reusable and was further reused for a bread baking operation when the opening of the container was displaced by 5 mm or less, while a container was regarded as no longer reusable when the opening of the container was displaced by more than 5 mm, and then the total number of times the container had been used was counted.

As seen in Table 2, each of the baking mold containers of Examples 1 to 9 was confirmed to be reusable a plurality of times.

TABLE 2 Baking Intermediate annealing Number of times temperature Thickness Temperature of use Example 1 150° C. 0.5 mm 300° C. 6 Example 2 180° C. 0.5 mm 300° C. 5 Example 3 200° C. 0.5 mm 300° C. 4 Example 4 150° C. 1.2 mm 400° C. 5 Example 5 180° C. 1.2 mm 400° C. 5 Example 6 200° C. 1.2 mm 400° C. 4 Example 7 150° C. 0.5 mm 300° C. 3 Example 8 180° C. 0.5 mm 300° C. 3 Example 9 200° C. 0.5 mm 300° C. 2

Next, an aluminum alloy piece in the alloy composition shown in Table 1 was obtained by continuous casting, and then plate-rolled into a 0.5 mm thick aluminum alloy piece, which was then subjected to intermediate annealing at a temperature of 300° C. for five hours. A resultant aluminum alloy foil having a thickness of 75 μm was obtained as Example 10.

In addition, an aluminum alloy piece in the alloy composition shown in Table 1 was obtained by continuous casting, and then plate-rolled into a 1.2 mm thick aluminum alloy piece, which was then subjected to intermediate annealing at a temperature of 400° C. for five hours. A resultant aluminum alloy foil having a thickness of 75 μm was obtained as Example 11.

In a similar manner, an aluminum alloy piece in the alloy composition shown in Table 1 was obtained by continuous casting, and then plate-rolled into a 1.2 mm thick aluminum alloy piece, which was then subjected to intermediate annealing at a temperature of 170° C. for five hours. A resultant aluminum alloy foil having a thickness of 75 μm was obtained as Comparative Example 1.

In addition, an aluminum alloy piece in the alloy composition shown in Table 1 was obtained by continuous casting, and then plate-rolled into a 0.5 mm thick aluminum alloy piece, which was then subjected to intermediate annealing at a temperature of 500° C. for five hours. A resultant aluminum alloy foil having a thickness of 75 μm was obtained as Comparative Example 2.

Examples 10 and 11 and Comparative Examples 1 and 2 were evaluated in terms of tensile strength and elongation. Results are shown in Table 3 below.

The aluminum alloy foil was evaluated as “∘” if it maintained a tensile strength of at least 120 N/mm² with an elongation of at least 3.0% when subjected to softening treatment at 150° C. for a maximum of 240 minutes; otherwise the aluminum alloy foil was evaluated as “x”.

Likewise, the aluminum alloy foil was evaluated as “o” if it maintained a tensile strength of at least 100 N/mm² with an elongation of at least 3.0% when subjected to softening treatment at 180° C. for a maximum of 240 minutes; otherwise the aluminum alloy foil was evaluated as “x”.

In addition, the aluminum alloy foil was evaluated as “0” if it maintained a tensile strength of at least 90 N/mm² with an elongation of at least 3.0% when subjected to softening treatment at 200° C. for a maximum of 240 minutes; otherwise the aluminum alloy foil was evaluated as “x”.

This is due to the fact that an aluminum foil usually needs to have an elongation of at least 2.0% in order to be formed into a container by deep drawing.

TABLE 3 Intermediate annealing Plate Foil heating temperature thickness Temperature 150° C. 180° C. 200° C. Example 10 0.5 mm 300° C. ∘ ∘ ∘ Example 11 1.2 mm 400° C. ∘ ∘ ∘ Comparative 1.2 mm 170° C. x x x Example 1 Comparative 0.5 mm 500° C. x x x Example 2

The aluminum alloy foils of Examples 10 and 11 and Comparative Examples 1 and 2 were heated by using a generally used heater, and changes in tensile strength (N/mm²) and elongation (%) were measured in relation to heating time. Results are shown in FIGS. 1 to 6.

FIGS. 1 and 2 show tensile strength and elongation levels of the aluminum alloy foils subjected to a heating temperature of 150° C. FIGS. 3 and 4 show tensile strength and elongation levels of the aluminum alloy foils subjected to a heating temperature of 180° C. FIGS. 5 and 6 show tensile strength and elongation levels of the aluminum alloy foils subjected to a heating temperature of 200° C.

In each figure, a line plotted with ▪ represents Example 10, a line plotted with ▴ represents Example 11, a line plotted with ♦ represents Comparative Example 1, and a line plotted with x represents Comparative Example 2.

As seen in the individual figures, in the case of heating at 150° C. for a maximum of 240 minutes, Examples 10 and 11 maintained a tensile strength of at least 120 N/mm² (Example 10: about 170 N/mm², Example 11: about 130 N/mm² when heated for 240 minutes) and had an elongation of at least 2.0% (Example 10: about 3.5%, Example 11: about 6.5% when heated for 240 minutes).

In the case of heating at 180° C. for a maximum of 240 minutes, Examples 10 and 11 maintained a tensile strength of at least 100 N/mm² (Example 10: about 140 N/mm², Example 11: about 110 N/mm² when heated for 240 minutes) and had an elongation of at least 3.0% (Example 10: about 7.5%, Example 11: about 8.0% when heated for 240 minutes).

In the case of heating at 200° C. for a maximum of 240 minutes, Examples 10 and 11 maintained a tensile strength of at least 90 N/mm² (Example 10: about 130 N/mm², Example 11: about 110 N/mm² when heated for 240 minutes) and had an elongation of at least 3.0% (Example 10: about 6.5%, Example 11: higher than 8.0% when heated for 240 minutes).

In contrast, Comparative Example 1 exhibited lack of a desired elongation as seen in FIGS. 2, 4, and 6, which show an elongation lower than 2.0% in the case of heating at 150° C. for a maximum of 240 minutes, an elongation lower than 3.0% in the case of heating at 180° C. for a maximum of 240 minutes, and an elongation lower than 3.0% in the case of heating at 200° C. for a maximum of 240 minutes.

Comparative Example 2 exhibited lack of a tensile strength desired to the aluminum alloy of the present invention, namely the tensile strength of 75 N/mm², which is lower than 90 N/mm² in the case of heating at 200° C. for a maximum of 240 minutes, although the tensile strength when heated at 150° C. for a maximum of 240 minutes exceeds 120 N/mm² and the tensile strength when heated at 180° C. for a maximum of 240 minutes exceeds 100 N/mm², as seen in FIGS. 1, 3, and 5.

The embodiments and examples disclosed herein are to be regarded in every respect not as restrictive but as illustrative. The scope of the present invention is defined by the included claims, and is intended to include all modifications and variations falling within the meaning and scope equivalent to the scope of the claims. 

1. An aluminum alloy foil that: maintains a tensile strength of at least 120 N/mm² and has an elongation of at least 2.0% when subjected to softening treatment at 150° C. for a maximum of 240 minutes; maintains a tensile strength of at least 100 N/mm² and has an elongation of at least 3.0% when subjected to softening treatment at 180° C. for a maximum of 240 minutes; and maintains a tensile strength of at least 90 N/mm² and has an elongation of at least 3.0% when subjected to softening treatment at 200° C. for a maximum of 240 minutes.
 2. The aluminum alloy foil according to claim 1, comprising: 0.3 to 3.0 mass % iron; 0.8 to 1.5 mass % silicon; 0.0001 to 0.011 mass % copper; 0.0001 to 0.6 mass % manganese; 0.0001 to 0.011 mass % magnesium; 0.001 to 0.011 mass % zinc; 0.005 to 0.5 mass % titanium; and 0.0001 to 0.3 mass % zirconium, with a balance being aluminum and inevitable impurities.
 3. The aluminum alloy foil according to claim 1, wherein the aluminum alloy foil is subjected to intermediate annealing at a temperature of 300° C. to 400° C. during plate-rolling into a thickness of 0.5 to 1.2 mm after continuous casting.
 4. The aluminum alloy foil according to claim 2, having a thickness of 5 to 100 μm.
 5. An aluminum container comprising the aluminum alloy foil according to claim
 2. 6. A method for producing an aluminum alloy foil, the method comprising: preparing an aluminum alloy comprising: 0.3 to 3.0 mass % iron; 0.8 to 1.5 mass % silicon; 0.0001 to 0.011 mass % copper; 0.0001 to 0.6 mass % manganese; 0.0001 to 0.011 mass % magnesium; 0.001 to 0.011 mass % zinc; 0.005 to 0.5 mass % titanium; and 0.0001 to 0.3 mass % zirconium, with a balance being aluminum and inevitable impurities; forming the aluminum alloy into an aluminum alloy piece through continuous casting; plate-rolling the aluminum alloy piece into an aluminum alloy plate having a thickness of 0.5 to 1.2 mm; carrying out intermediate annealing at a temperature of 300 to 400° C. during the plate-rolling step; and foil-rolling the aluminum alloy plate into an aluminum alloy foil having a thickness of 5 to 100 μm. 